In a printing apparatus, such as an inkjet printing apparatus with a plurality of printing heads arranged in a transportation direction of a printing sheet, transportation of the printing sheet in a skew or serpentine manner causes misregister that a printing position is shifted orthogonally to the transportation direction. Such misregister degrades a printing quality. Consequently, a challenge for the printing apparatus is to determine and correct a shift amount in the misregister.
A currently-used inkjet printing apparatus for printing in a plurality of colors adopts the following approach for determining a color misalignment amount and a correction amount of the color misalignment occurring due to the skew or serpentine transportation of the printing sheet. That is, evaluation patterns are printed on a plurality of given printing sheets successively. The patterns are visually determined partially using a magnifying glass or are determined using a special measuring instrument, whereby an average shift amount is determined and a correction amount of the shift amount is calculated. Thereafter, the inkjet printing apparatus is adjusted with the correction amount. This is typically performed. See, for example, Japanese Patent Publication No. 2003-341016A.
However, the examples of the conventional apparatus with such constructions have the following problems.
Specifically, the currently-used approach is complicated in terms of determining the correction amount. Accordingly, the approach involve a problem that much time is required for obtaining the correction amount used for correcting the misregister due to the skew or serpentine transportation.
Likewise the misregister due to the skew or serpentine transportation, the approach also involves a problem that much time is required for obtaining a correction amount used for correcting misregister in the transportation direction. Here, the misregister in the transportation direction means a deviation in discharge timing of ink droplets in an inkjet printing apparatus. Alternatively, the misregister also occurs from a variation in transportation speed of the printing sheet.